Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image of an original document being reproduced. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Two component and single component developer materials are commonly used. A typical two component developer material has magnetic carrier granules with toner particles adhering triboelectrically thereto. A single component developer material typically comprises toner particles. Toner particles are attracted to the latent image forming a toner powder image on the photoconductive member. The toner powder image is subsequently transferred to a copy sheet. Finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
One type of single component development system is a scavengeless development system that uses a donor roll for transporting charged toner to a development zone. A plurality of electrode wires are closely spaced to the donor roll in the development zone. An AC voltage is applied to the wires forming a toner cloud in the development zone. The electrostatic fields generated by the latent image attract toner from the toner cloud to develop the latent image. A hybrid scavengeless development system employs a magnetic brush developer roller for transporting carrier having toner adhering triboelectrically thereto. The donor roll and magnetic brush roll are electrically biased relative to one another. Toner is attracted to the donor roll from the magnetic brush roll. The donor roll transports the charged toner to a development zone. The electrically biased electrode wires detach the toner from the donor roll forming a toner powder cloud in the development zone, and the latent image attracts the toner particles thereto. In this way, the latent image recorded on the photoconductive member is developed with the toner particles. It has been found that streaks are formed in the developed latent image when debris is trapped in, or when toner and/or toner constituents builds up on the electrode wires. Heretofore, the electrode wires have been positioned substantially perpendicular to the process direction, i.e. substantially parallel to the longitudinal axis of the donor roll. Various types of development systems have hereinbefore been used incorporating electrode wires as illustrated by the following disclosures, which may be relevant to certain aspects of the present disclosure.
U.S. Pat. No. 4,868,600 describes an apparatus wherein a magnetic roll transports two component developers to a transfer region where toner from the magnetic roll is transferred to a donor roll. The donor roll transports the toner to a region opposed from a surface on which a latent image is recorded. A pair of electrode wires are positioned in the space between the surface and the donor roll and are electrically biased to detach toner from the donor roll to form a toner cloud. Detach toner from the cloud develops the latent image.
U.S. Pat. No. 4,984,019 discloses a developer unit having a donor roll with electrode wires disposed adjacent thereto in a development zone. A magnetic roll transports developer material to the donor roll. Toner particles are attracted from the magnetic roll to the donor roll. When the developer unit is inactivated, the electrode wires are vibrated to remove contaminants therefrom.
U.S. Pat. No. 5,422,709 teaches an apparatus in which a donor roll advances toner to an electrostatic latent image recorded on a photoconductive member. A plurality of electrode wires are positioned in the space between the donor roll and the photoconductive member. The electrode wires extend in a transverse direction relative to the longitudinal axis of the donor roll. The electrode wires are electrically biased to detach the toner from the donor roll so as to form a toner cloud in the space between the electrode wires and photoconductive members. Detached toner from the toner cloud develops the latent image. Electrode wires contact a portion of the surface of the donor roll. As the donor roll rotates, friction between the electrode wires and donor roll causes trapped debris to move away from the toner powder cloud region so as to minimize contamination produced streaks on the developed image.
U.S. Pat. No. 7,383,973, issued Jun. 10, 2008, by Edward A. Enyedy and entitled WIRE MODULE FOR DEVELOPER UNIT discloses a wire feeding mechanism for advancing a continuous length of wire along a pathway includes a housing having two roller supports each rotatable about a corresponding axis transverse to a wire pathway. The roller supports are on opposite sides of the pathway and are driveably engaged with each other. A drive roller is on each of the roller supports for rotation therewith. The drive roller includes an outer surface extending circumferentially about the corresponding axis. The outer surface defines a groove having an included angle of less than ninety degrees (90°). The drive roller on each of the roller supports compressively contacts a continuous length of wire between the roller supports such that the wire is advanced along the pathway in response to rotation of the drive rollers.
U.S. Pat. No. 7,076,193, issued Jul. 11, 2006, by Wing et al., and entitled “DRIVE ROLLERS FOR WIRE FEEDING MECHANISM” discloses an apparatus for developing in a development zone a latent image recorded on a surface, including a housing defining a chamber storing at least a supply of toner therein; a donor member disposed of at least partially in the chamber of the housing and spaced from the surface, the donor member being adapted to rotate about a longitudinal axis to transport toner to the development zone in a region opposed from the surface; and a wire assembly module mounted the development zone and extending in a direction transverse to the longitudinal axis, the wire assembly module including a wire and a drive system for translating portions of the wire in the development zone, and power supply for electrically biasing the wire to detach toner from the donor member so as to form a toner powder cloud in the development zone with detached toner from the toner cloud developing the latent image.
A problem with developer systems using wires is that toner and/or toner constituents buildup on the wires over time and result in development defects. Wire contamination is a first class of defect in which toner and/or toner constituents build up on the wire side that is in contact with the donor roll. Wire history is a second class of defect in which toner and/or toner constituents build up on the wire side away from the donor roll. Wire history involves highly charged (though sometimes low charged) and generally small toner or other particles being attracted to the wire and sticking to the wire as a result of either adhesive or electrostatic attractive forces. The result is that contaminants build up on the electrodes, as a response to the image area coverage history, causing visible streaks on prints. Constant cleaning of the wires is required in order to alleviate the above-defects, which cleaning is time-consuming and inefficient in that it requires machine downtime.
Another problem is in machines which require large development zones that the width of the donor roll is such that a very large number of those wires are required to cover the whole printable area. The wrapping of this many wires poses very serious manufacturability challenges. In addition, the wires must all be supported at exactly the same tension which must be maintained. This poses both a design and manufacturability challenge, when either a single wire or a plurality of wires is used.
The present disclosure and exemplary embodiments herein obviates the problems noted above by providing an apparatus for developing in a development zone a latent image recorded on a surface, including a housing defining a chamber storing at least a supply of toner therein; a donor member disposed of at least partially in the chamber of said housing and spaced from the surface, said donor member being adapted to rotate about a longitudinal axis to transport toner to the development zone in a region opposed from the surface; and a wire assembly module mounted in the development zone and extending in a direction transverse to the longitudinal axis, said wire assembly module including a wire and a drive/cleaning system for translating portions of the wire in the development zone and cleaning the wire, and a power supply for electrically biasing said wire to detach toner from said donor member so as to form a toner powder cloud in the development zone with detached toner from the toner cloud developing the latent image.